Effects of treadmill exercise on methadone withdrawal-induced locomotor sensitization and the ventral pallidum and ventral tegmental area BDNF levels in morphine withdrawn rats receiving methadone maintenance treatment

•MMT were mildly increased morphine-induced hyperlocomotion.•Exercise decreased morphine-induced hyperlocomotion in morphine-withdrawn rats.•The VP BDNF level was still higher in the exercising morphine-withdrawn rats.•Exercise had no effect on the locomotors response in rats receiving MMT.•Exercise had no effect on the VTA-VP BDNF levels in rats receiving MMT. This study examined the effects of treadmill exercise on the methadone withdrawal -induced locomotor sensitization, the ventral tegmental area (VTA) and ventral pallidum (VP) BDNF levels in morphine withdrawn rats receiving methadone maintenance treatment (MMT). The rats were chronically treated with bi-daily doses (10 mg/kg, at 12 h intervals) of morphine for 14 days. The exercising rats receiving MMT were forced to run on a motorized treadmill for 30 days during morphine withdrawal. Then, rats were exposed to a 14-day methadone withdrawal period, without any exercise and then challenged with morphine (1 mg/kg, ip) and evaluated for locomotor activity. Also, the VTA-VP BDNF levels were assessed before and after receiving MMT. The sedentary morphine-dependent rats receiving MMT and morphine-dependent rats receiving saline challenged to morphine exhibited a higher level of locomotor activity compared to Sal/Sal/Sed group after withdrawal of drug. While, the level of locomotor activity was lower in the D/Meth/Sed than in D/Sal/Sed rats. The VP BDNF level and the locomotors response were higher and lower, respectively in the D/Meth/Sed and D/Sal/Exc than the D/Sal/Sed rats. Exercise had no effect on the locomotors response and the VP BDNF levels in morphine-dependent rats receiving MMT. Our results showed that the sedentary morphine-dependent rats challenged to morphine enhanced the morphine-induced hyperlocomotion, whereas decreased the VP BDNF levels. MMT resulted in a persistent of locomotor sensitization caused by morphine withdrawal, though milder. Exercise had no effect on the locomotors response and the VTA-VP BDNF levels in the D/Meth/Exc.